1. Field of the Invention
The present invention relates to a plasma display panel, and more particularly, to a plasma display panel having an improved structure where sufficient air exhaustion can be achieved without sacrificing discharge efficiency.
2. Description of the Related Art
The plasma display panel is recently replacing the cathode ray tube (CRT) as a device for displaying images. In a plasma display panel, a discharge gas is filled between two substrates supporting a plurality of electrodes, a discharge voltage is applied to the electrodes in the panel to generate ultraviolet rays, and a phosphor layer of a predetermined pattern is excited by the ultraviolet rays to produce a visible image.
The plasma display panel can be classified into a direct current (DC) type and an alternating current (AC) type. In the DC type plasma display panel, electrodes are exposed in a discharge space so that electric charges move directly between corresponding electrodes. In the AC type plasma display panel, at least one side of the electrodes is covered with a dielectric layer, so that a discharge is achieved by movements of wall charges accumulated on the dielectric layer.
Since charges directly move between the corresponding electrodes in the DC type plasma display panel, the electrodes are severely damaged. In order to preserve the electrodes, the AC type plasma display panel having a three-electrode surface discharge type structure has been recently adopted.
In general, an AC type plasma display panel includes two substrates separated from each other and in parallel, and main barrier ribs defining a plurality of discharge cells forming an area producing the image. In addition, a phosphor layer is formed within the discharge cells defined by the main barrier ribs.
The phosphor layer can be formed in various ways, one being nozzle injection. Nozzle injection refers to a process where fluorescent material is ejected from a nozzle dispenser and is injected into the discharge cells. According to the nozzle injection method, fluorescent material in the form of a paste is injected into the discharge cells from a plurality of nozzles to form the phosphor layer to a predetermined thickness. One drawback of the nozzle injection method is that injection amount and injection pressure of the fluorescent material during the initial stage of the injection process is unstable and difficult to control, making it difficult to form a phosphor layer having a uniform thickness in each of the discharge cells. In order to overcome this problem, the fluorescent material can be injected into the discharge cells after the injection amount and injection pressure of the fluorescent material stabilizes so that a phosphor layer of uniform thickness can be formed in each discharge cell. In order to stabilize the injection amount and injection pressure of the fluorescent material at early stage of injection, a buffer period should be employed. When a buffer period is employed, dummy barrier ribs are formed on outer portions of the outermost main barrier ribs. The dummy barrier ribs define dummy cells at the outer portion of the outermost discharge cells discharge cells after the injection amount and injection pressure of the fluorescent material stabilizes so that a phosphor layer of uniform thickness can be formed in each discharge cell. In order to stabilize the injection amount and injection pressure of the fluorescent material at early stage of injection, a buffer period should be employed. When a buffer period is employed, dummy barrier ribs are formed on outer portions of the outermost main barrier ribs. The dummy barrier ribs define dummy cells at the outer portion of the outermost discharge cells.
The dummy cells defined by the dummy barrier ribs serve as buffers that serve to stabilize the injection amount and injection pressure of the fluorescent material. The fluorescent material can be injected first into the dummy cells at the initial stage of injection process when the injection amount and injection pressure are not stabilized.
Then, when the injection amount and injection pressure has stabilized, the fluorescent material is injected into the discharge cells which are located in the area where the image is displayed. By doing so, the thickness of the phosphor layer within the discharge cells can be better controlled so that a uniform thickness is achieved for every discharge cell. In this scenario, the dummy cells need to be sufficiently large so that stabilization of the injection amount and injection pressure occurs when the fluorescent material is injected into the discharge cells.
However, in order ensure that there is sufficient space for the dummy cells, the dummy barrier ribs are formed to extend adjacent to a sealing member that seals the two substrates. When this is done, spaces between the dummy barrier ribs and the sealing member tend to become too small so that air exhaustion through a space between the dummy barrier ribs and the sealing member cannot be satisfactorily achieved. As a result, impurities remain in the panel, causing the discharge voltage to rise, resulting in mis-discharging, which leads to a decrease in the discharge efficiency. Therefore, what is needed is a design for a plasma display panel where there is sufficient space for the dummy barrier ribs so that the fluorescent material in each of the discharge cells can be formed to the same thickness, the design also being able to allow for satisfactory air exhaustion so that the problems of mis-discharging and decrease in discharge efficiency can be avoided.